1. Field of the Invention
The current invention generally relates to computing systems. More specifically, the present invention relates to making saving power in memory by collecting real pages into fewer and/or lower powered real memory portions.
2. Description of the Related Art
Computing systems include a wide range of data processing systems, including Personal Digital Assistants (PDAs), laptop computers, desktop computers, midrange computers, and mainframe computers. Reduction of power consumption is a very important design consideration in development of computing systems. In the laptop market, a reduction in power translates to a longer time period the laptop can be used before a battery in the laptop must be recharged. Alternatively, for a laptop computing system, reduced power consumption can translate into a smaller, cheaper, lighter, battery requirement. In computing systems that are “plugged in” (i.e., connected to an external source of power), a reduction in power translates into cooler, more reliable operation, smaller and/or cheaper power supplies, reduced cooling requirements, or a combination of the above. Reduced electrical bills for a user of the computing system is a marketing advantage for the computing system having lower power requirements for a given level of performance (throughput) of the computing system.
Computing systems typically contain relatively large amounts of volatile storage in the form of static random access memory (SRAM) and dynamic random access memory (DRAM). Recent advances in DRAM technology have included a “Deep Power Down” mode (DPD). Existing computing systems are generally unable to utilize the DPD mode because an operating system in the computing system distributes pages across the entire real memory in the computing system. Placing a real memory portion into the DPD mode causes loss of all data contained within the DRAM. Volatile memory is memory that loses all data contained within that memory when power is removed, either by shutting the memory off or by placing the memory into the DPD mode.
Therefore, there is a need for a method and apparatus that allow use of DPD in computing systems without loss of data.